Summary of the hydroDynamic Problem of small yachts at sea

[CarlosK2]

Ocean Prediction Center, 500 MB

Year after year, it's curious to observe that in the end, the fundamental variables are location and dates.

They knew they were in the Mediterranean at the end of summer ?

This is just days before the capsizing of the large motor vessel "Bayesian."

 

[CarlosK2]

For example

To avoid crossing waves in January, one could cross by sailing south from the Canary Islands to Cape Verde

And to avoid an F10 demolition derby, one could return in March, staying below 30 degrees North and even avoiding the Azores.

 

[CarlosK2]

The 500 MB chart is the mariner's chart

There are guides out there to help you understand it, but you end up with cold feet and a hot head

Mariners Weather Log Vol. 52, No. 3, December 2008 https://www.vos.noaa.gov/MWL/dec_08/milibar_chart.shtml

Simple guide:

a) The thick underlined line marks the Force 8 boundary

But note that at the top left (underlined in red) at altitude there are indications of 80 knots of wind which would be about 40 knots on the surface of the sea

b) The surface wind is half the wind speed indicated at 500 MB heigh

c) If the lines point north... Achtung !

This is an extraction chimney into the jet stream, and the surface wind tends to equalize with the wind speed above at 500 MB

And

And we also have to take into account the sea temperature (!)

A perfect explosive cocktail

Ted Fujita - Wikipedia https://en.wikipedia.org/wiki/Ted_Fujita

 

[CarlosK2]

In Summary

2 Seaworthiness and Safety at Sea, CA Marchaj "Seaworthiness. The Forgotten Factor":

"It is known (...) that one can go to sea on a raft, or any other bizarre craft, and survive if the gods are merciful and willing (...) Odysseus survived because he was a favorite of Zeus (...) [but] (...) Since not every mortal is equally favoured by the gods ..."

In other words, in the end it's a matter of comfort or discomfort and greater or lesser peace of mind.

 

[CarlosK2]

CA Marchaj, "Seaworthiness. The Forgotten Factor"

The funny thing

His fierce diatribe against the modern yacht, culminating in Fastnet in 1979, wasn't critical enough, because the problem with those yachts was their enormous imbalance on the two fundamental axes, pitch and yaw, and therefore their inability to surf in a controlled and safe manner

And yet, his criticism is accurate regarding the passive safety of the wide, lightweight surfboards that the Mini Transat brought us from 1979 onwards, solving the hydrodynamic problem of the small yacht on the open sea.

 

[CarlosK2]

"Galatea" vs "Mayflower"

The old debate (ca. 1850-1900) between the British and Americans remains relevant, and to understand it we must listen to both points of view.

In fact, someone could argue that the "Zinzolin," sailing at 10 knots, lacked speed and that under those conditions, its speed as a real windsurf board would be 17 knots

but there is no doubt that the capsizing of the IMOCA "Hugo Boss" and the Pogo 8.50s "Yum" and "Zinzolin" vindicates the old fogey viewpoint: waves easily capsize wide and light boats.

 

[CarlosK2]

2) Passive safety
2B) Wave impact

We're not going back to very narrow yachts; but we have to be aware that with wide, lightweight surfboards we solve a hydrodynamic problem (big wave surfing) and create a weakness

My peace treaty between the British and Americans focuses on B/D =< 2

CA Marchaj, "Seaworthiness. The Forgotten Factor"

(Notice in the video how water comes out of the mast when the yacht rights up)

A moderate hull shape is a good start. Keep in mind that a B/D of 1.95 would have scandalized the old British as an extreme sloop.

 

[CarlosK2]

In the video, we can see excellent passive safety at point 2B) the impact of a Wave

And in other videos, we see wide, light sailboats surfing beautifully, the hydrodynamic problem solved, active safety 3C) Surfing

All that's needed is a little more effort to stay on course by holding both ends of the rope.

 

[CarlosK2]

Whether it's an old, second- or third-hand boat worth 4,000 euros or a brand-new sports yacht costing 400,000 euros (with living space like a tent that no "lady" would call a "home") ... the principles for solving the hydrodynamic problem are the same:

1) Pitch-A control (wave arrival from the stern): good longitudinal balance: hydrostatic in the snail-yacht, largely hydrodynamic in the sports-yacht

2) Yaw control

3) Pitch-B control: good hull attitude (bow up, stern down) for surfing when accelerating, propelled by the Force of the Sea, the Force of the Wind, and the Force of the Earth

The point, therefore, is that yachts with good passive safety should learn to surf, and yachts that surf should learn to have good passive safety.

 

[CarlosK2]

I remember when we used to set sail in small dinghies (470) from a beach with waves

It was quite an adventure, and we stopped doing it after a mast broke

We'd drag them out to sea with a rope by the bow, jumping over the breaking waves

I remember when a breaking wave would snatch the boat from our hands ... the boat would be dragged sideways until it hit the water. This coincides exactly with what Andrew Claughton observed while experimenting with models in the Southampton wave channel: when the deck bites into the water, that's the crucial moment. In other words,

in stability curves (which date back to the 17th century and assume heeling is caused by the wind), it's often forgotten that with small and light yachts we have to imagine the yacht being pushed, and that a critical factor, as many sailors have pointed out, is the ability to slide, to glide, sideways.

The first line of defense, therefore, is a good freeboard built with a vertical topside and a low chine (which, incidentally, coincides with the current trend): in a light boat, this would allow it to float high even with a significant heel and be able to slide sideways

The second line of defense, to help the boat right itself, is a fully closed mast, which has a tremendous effect on a small, light boat

And the last line of defense is a cockpit that, when capsized, doesn't become the two hulls of a catamaran

Thus, a 1-ton ocean Windsurf Board Plywood Epoxy with 1 sailor (whether a young adventurer or a grumpy old man) maybe has a good chance of surviving the impact of a wave that crosses its path during its rapid flight.

 

[CarlosK2]

Marchaj, at the end of his book (where he unfolds his fierce critique of the modern yacht) finally approaches tentatively the core of the hydro-Dynamic problem of the modern yacht:

"In the book Naval Architecture of Planing Hulls [Lindsay, Lord, Cornell Maritime Press, 1946] we find the following remarks, much pertinent to the matter at hand:

"A distinguishing characteristic of the hull suited for blue-water cruising (...) Adequate realization of both functions [direccional stability under difficult condition, and steering] is of primary importance (...)

the center of effective lateral plane area should coincide vertically with the boat's center of gravity" (...)"

and two pages later, almost at the end, it gets closer and closer to the problem:

"When the stern is lifted by an overtaking wave, the boat can easily be pivoted around her fin keel which is well forward, so that she goes into a rapid broach and is rolled by the sea*

[And in a footnote]

* If the bow is depressed and the stern lifted up the centre of lateral resistance of the hull moves rapidly forward"

E x a c t l y

But the book ends right joyfully welcoming the appearance of the first version of van Oossanen (hydro-Static) Stability Index (STIX)

 

[CarlosK2]

Note the paradox

In Fastnet 1979, modern yachts that couldn't surf reached their peak, while American Express, in 1979, showed us the new path with the Mini Transat.

Meanwhile, a belief spreads endlessly: those modern yachts lacked hydro-Static stability.

And meanwhile, magnificent wide and lightweight surfboards emerged that, now, capsized and didn't right themselves like Grimalkin did time and again after capsizing.

 

[CarlosK2]

(> 300 K Euros)

Let's be honest

A €400,000 sports yacht is a toy for a man; no woman in her right mind would call that a "yacht."

And what's more, for once, the universe is on the side of the little guy

Square–cube law - Wikipedia https://en.wikipedia.org/wiki/Square%E2%80%93cube_law

So let's simplify things (half the issue, anyway): if there are ocean rowing boats, why can't there be ocean windsurf boards ... capable of righting themselves after capsizing

LCF: longitudinal position of the Center of Flotation when attempting to surf a big wave
0.5 Froude number
A: hydro-Dynamic Lift
LCG: Longitudinal position of the Center of Gravity
HC_K: hydro-Dynamic Center of the Keel